Acids and bases
The famous fench chemist Lavoisier proposed in 1777 that oxygen was the universal icidifying principle. He belived that an acid could be defined as a compound ofoxygen and a non-metal. In fact the name he gave to the newly discovered gas oxygen means ‘acid former’. This theory, however, had ti be dismissed when the acid HCl was proved to be made of hydrogen andchlorine only- with no oxygen.
A bif step forward came in 1887 when the Swedish chemist Arrhenius suggested that an acid could be defined as a substance that dissociates in water to form hydrogenIons and anions, while a base dissociates into hydroxide ions and cations.
Bronsted-Lowry: a theory of proton transfer
In 1923 two chemists, martin lowry of Cambridge, England and Johannes Bronsted ofCopenhagen, Denmark, Independently published similar conclusions regarding the definitions of acids and bases. Their findings overcame the limitations of Arrhenius work and have become established asthe Bronsted-Lowry theory. This theory focuses on the transfer of H+ ions during an acid-base reaction:acids donate H+ while bases accept it.
The theory can be stated as:
* A bronsted-lowry acidis a proton (H+) donor
* A Bronsted-Lowry base is a proton (H+) acceptor
The act of donating cannot happen in isolation- There must always be something present to play the roleof acceptor. In Bronsted-lowry theory, an acid can therefore behave as a proton donor if there is also a base present to accept the proton.
Lewis: a theory of electron pairs
Gilbert lewis, whosename famously belongs to electron dot structures for representing covalent bonding, used such structures in interpreting brontsed-lowry theory. Realizing that the base must have a line pair ofelectrons, he reasoned that the entire reaction could be viewed in terms of electron pair rather than in terms of proton transfer.
Properties of acids and bases
While we have seen that ideas regarding...
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